PINGUICULA. 345 



have been shown to be sensitive, and on touching them the 

 valves close. By this plant minute water-insects and crusta- 

 ceans are captured (see Fig. 190). 



Drosophyllum, a rare plant found in Portugal, catches insects 

 by a viscid secretion from minute mushroom-shaped glands. 

 The tentacles do not have the power of movement possessed 

 by those of Drosera. That its glands can secrete a digestive 

 fluid appears from Mr. Darwin's experiments. 



Roridula, found at the Cape of Good Hope, and Byblis, of 

 western Australia, closely resemble the viscid-haired Droseraceae, 

 which have been examined in a fresh state, and they have been 

 added to the list of the insect-catching plants of the order. 



904. Pinguicula is so called from the greasy appearance pre- 

 sented by the upper surface of its leaf, due to the existence of 

 great numbers of disc-like glandular hairs with short stalks. 

 The glandular character of the hairs is shown by the secretion 

 which exudes from them even when they are not irritated. 



905. The secretion which flows when the leaves of Pinguicula 

 are not excited by the presence of albuminous matter is neutral ; 

 but upon excitation of the leaf it becomes acid, far more copious 

 in amount, and has the power of digesting nitrogenous organic 

 substances. At that time the clear contents of the cells of the 

 glands also become aggregated, much as in the case of the cells 

 in Drosera ; and this fact is adduced by Darwin as proof that the 

 digested matters are absorbed. 



906. In about three hours after an insect 

 alights upon a leaf of Pinguicula the margin 

 begins to roll over it and envelop it, in the 

 manner shown by the accompanying figure. 

 The following experiment by Darwin shows 

 what takes place in this incurving: "A young 

 and almost upright leaf was selected with its 

 two lateral edges equally and very slightly in- 

 curved. A row of small flies was placed along 

 one margin. When looked at next day, after 

 fifteen hours, this margin but not the other was 

 found folded inwards, like the helix of the human 

 ear, to the breadth of one tenth of an inch, so 

 as to lie partly over the row of flies. The 



glands on which the flies rested, as well as those on the over- 



Fio. 157. Pinguicula vulgaris. Outline of leaf with its left margin inflected over a. 

 row of small flies. (Darwin . ) 



